This section is intended to provide a background or context to the invention disclosed below. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise explicitly indicated herein, what is described in this section is not prior art to the description in this application and is not admitted to be prior art by inclusion in this section. Abbreviations that may be found in the specification and/or the drawing figures are defined below, after the main part of the detailed description section.
U.S. patent application Ser. No. 12/927,663, filed Nov. 19, 2010 and U.S. Pat. No. 9,313,599 B2, issued Apr. 12, 2016, which are incorporated by reference herewith, describe mechanisms for ensuring backwards compatibility. That is, these references describe, for example, the ability to render an audio signal with conventional playback methods, such as stereo, for a spatial audio system.
U.S. Pat. No. 9,055,371 B2, issued Jun. 9, 2015, which is incorporated by reference herewith, describes a method for obtaining spatial audio (binaural or 5.1) from a backwards compatible input signal comprising left and right signals and spatial metadata. In accordance with this reference, original Left (L) and Right (R) microphone signals are used as a stereo signal for backwards compatibility. The (L) and (R) microphone signals can be used to create 5.1 surround sound audio and binaural signals utilizing side information. This reference also describes high quality (HQ) Left ({tilde over (L)}) and Right ({tilde over (R)}) signals used as a stereo signal for backwards compatibility. The HQ ({tilde over (L)}) and ({tilde over (R)}) signals can be used to create 5.1 surround sound audio and binaural signals utilizing side information. This reference also describes a method for ensuring backwards compatibility where a two channel spatial audio system can be made backwards compatible utilizing a codec that can use regular Mid/Side-coding, for example, ISO/IEC 13818-7:1997. Audio is inputted to the codec in a two-channel Direct/Ambient form. The typical Mid/Side calculation is bypassed and a conventional Mid/Side-flag is raised for all subbands. A decoder decodes the previously encoded signal into a form that is playable over loudspeakers or headphones. A two channel spatial audio system can be made backwards compatible where instead of sending the Direct/Ambient channels and the side information to the receiver, the original Left and Right channels are sent with the same side information. A decoder can then play back the Left and Right channels directly, or create the Direct/Ambient channels from the Left and Right channels with help of the side information, proceeding on to the synthesis of stereo, binaural, 5.1 etc. channels.
Typically, the prior attempts for backwards compatibility do not handle the situation where the audio signal or the side information has been tampered with.
Accordingly, there is a need for ensuring high quality playback and determining if an audio signal and related information transited in an audio stream has been tampered with, and if tampering is suspected or determined, an alternative playback mode made available.